In recent years, wind turbines have been integrated into electric power generation systems to create electricity to support the needs of both industrial and residential applications. These wind turbines capture the kinetic energy of the wind and convert it into electricity. A typical wind turbine includes a set of two or three large blades mounted to a hub. Together, the blades and hub are referred to as the rotor. The rotor is connected to a main shaft, which in turn, is connected to a generator. When the wind causes the rotor to rotate, the kinetic energy of the wind is captured and converted into rotational energy. The rotational energy of the rotor is translated along the main shaft to the generator, which then converts the rotational energy into electricity.
Historically, different types of generators have been used in wind turbines, such as a synchronous induction generator, a double wound induction generator, and a wound field synchronous induction generator. Each has its own advantages and drawbacks. Utilizing a synchronous induction generator is simple; however, it is physically large and not very efficient. The double wound induction generator is capable of increased efficiency; however, there are added costs and complexity involved. The wound field synchronous generator is similar to the synchronous induction generator in that it is simple to use but physically large and not very efficient.
As of late, design engineers have looked to variable speed permanent magnet generator systems. These systems allow the wind turbine to operate at an optimum rotational speed for the prevailing wind conditions, thereby increasing the efficiency of the energy capture. The permanent magnet generator system has been the most efficient means of converting the mechanical shaft power of the wind turbine into electrical energy. However, drawbacks to the conventional permanent magnet generator systems include: added complexity, added expense due to the costs of the supplementary high power rectifier and high power inverter, and reduced reliability due to the full power electronics.
Thus, there exists a need for a simplified, inexpensive and reliable permanent magnet generator system. This invention is directed to solving this need and provides a way to reduce the cost and complexity of the permanent magnet generator system for wind turbine applications.